This is a proposal to continue studies of the physiological properties of normal neuroglial cells in the mammalian cerebral cortex, and of hypertrophied reactive astrocytes in injured brain. Emphasis is placed on the electrophysiological characterization of neuroglial cells by means of their intracellularly recorded response to the activation of adjacent neurons, and by measurement of their electrical properties with intracellularly injected currents. Anatomical identification of electrophysiologically characterized cells is carried out with dye-injection techniques. The specific aims of the investigation are the study of passive and active properties of normal and of reactive glial cells, and the investigation of the functional relationship of these properties to neuronal activity, and to the regulation of the ionic environment of the brain. The major methods used to investigate glial properties are iontophoretic techniques of modifying their intracellular ionic content and their extracellular ionic environment and physical and chemical technqiues of decreasing and stimulating cellular metabolism.